U.S. Pat. Nos. 4,629,676 (Hayakawa et al) and No. 4,859,568 (Takeda) disclose an image forming method comprising the steps of imagewise exposing to light a light-sensitive material, and heating the light-sensitive material. The light-sensitive material comprises a support and a light-sensitive hardening layer containing silver halide, a reducing agent and a polymerizable compound. The light-sensitive material is heated to develop the silver halide and to harden the polymerizable compound.
U.S. Pat. Nos. 5,122,443 (Takeda), No. 5,290,659 (Takeda) and No. 5,393,651 (Hoshi) disclose embodiments of the above-mentioned light-sensitive material, which are advantageously used for the preparation of a lithographic plate. U.S. Pat. Nos. 5,304,454 (Yokoya et al), No. 5,326,667 (Yokoya et al) and No. 5,328,800 (Yokoya et al) disclose other embodiments of the light-sensitive material, which are advantageously used for the preparation of a color proof. In the light-sensitive materials for the lithographic plate or the color proof, a cross-linkable polymer can be used in place of or in addition to the polymerizable compound. Further, the light-sensitive hardening layer preferably comprises a hardening layer containing the polymerizable compound or the cross-linkable polymer and a light-sensitive layer containing silver halide. An overcoating layer containing a base precursor may be provided on the light-sensitive layer.
In the above-mentioned image forming methods, some components of the light-sensitive material form a gas. In the case that an acylhydrazine compound (disclosed in U.S. Pat. No. 4,859,568) is used as a reducing agent, the oxidation product of the compound forms nitrogen gas after reducing silver halide. Further, the base precursor is usually in the form of a carboxylic acid and a base. The carboxylic acid in the base precursor is decarboxylated under heating to release carbon dioxide gas as well as the base.